1. Field of the Invention
The present invention relates to a vehicular steering column of a low tilt type, supported to a body at upper and lower portions thereof to be tilted in whole about a hinge joint located on the lower portion, and more particularly to a shock absorbing steering column designed to allow a steering column to slide forward when a vehicle driver gets a secondary shock against a steering wheel due to a vehicular collision, thereby absorbing a shock. In particular, the present invention is characterized in that, in order to absorb a shock in case of the vehicular collision, shock absorbing means is provided to a lower supporting structure of the steering column so that an initial shock imposed on the driver can be greatly decreased.
2. Background of the Related Art
Such a steering column of the low tilt type is generally supported to a body at upper and lower portions thereof. The upper supporting structure is provided with a tilt unit for providing tilt operation of the steering column, while the lower supporting structure is provided with a hinge joint for allowing the steering column to be tilted in whole.
Because a vehicle driver frequently gets a secondary shock against the steering wheel when a vehicular collision occurs, the steering column must be designed to be capable of absorbing such a shock. Further, because of the vehicular collision, when being distorted at the front part, the body is deformed at the rear part where a driver is located. In this case, the steering column must be so designed that it is not pushed toward the driver if possible. To this end, a supporting structure of the steering column, which is fixed to the body, is constructed in a manner that the steering column performs a relative movement to the body when a predetermined shock is given. This construction can be implemented either by allowing the steering column to perform a relative movement to its own supporting structure when a shock is given, or by allowing the steering column and its own supporting structure to integrally perform a relative movement to the body.
For the foregoing purpose, a structure designed to allow the upper supporting structure of the steering column to be separated from the body when a vehicular collision occurs is disclosed from U.S. Pat. No. 5,899,116 as an example. Further, a structure designed to allow the steering column to perform a relative movement to its own supporting structure is disclosed from U.S. Pat. No. 6,019,391 as an example.
Further, a structure designed to allow a predetermined metallic strap to generate plastic deformation to absorb a shock when the steering column and the body carry out a relative movement to each other due to a collision is disclosed from U.S. Pat. Nos. 5,706,704 and 5,720,496 as examples.
Meanwhile, among the steering columns of the low tilt type, there is one comprising a means for absorbing a shock, which is provided to the lower supporting structure of the steering column. This conventional shock absorbing steering column, for example, is disclosed from GB Patent No. 2365826 (see FIGS. 1 and 2).
The structure as above is comprised of a bracket B fixedly attached to the body, a tilt steering supporting structure A fixedly attached to a steering column and provided with a slot A1, and a pivoting member 10 connecting the bracket B and the tilt steering supporting structure A. The slot A1 is formed with a predetermined partition member 4, thus preventing the pivoting member 10 from being deviated in place. In this case, when a shock is applied to the steering column due to a vehicular collision, the pivoting member 10 deforms the partition member 4 to slide along the slot A1, so that the shock can be absorbed.
However, the structure as above has a problem in that the shock is not appropriately absorbed, because the bracket B is stiffly fixed to the body. To be more specific, a process of giving a shock to a vehicle driver when the vehicle driver strikes the steering wheel is divided into two steps.
The first step is one occurring while the pivoting member 10 deforms the partition member 4 formed at the slot A1. The second step is one occurring while the pivoting member 10 slides along the slot A1. In the second step, the steering column slides in its own way to move forward, so that the shock is well absorbed. As a result, the shock given to the driver becomes still more decreased.
However, in the first step, the partition member 4 formed at the slot A1 functions to strongly support the shock of the driver against the steering wheel until the partition member 4 is deformed by the pivoting member 10, so that the shock of the driver who strikes the steering wheel can not be properly absorbed. Therefore, the conventional structure as above has a problem in that an initial shock generated when the driver strikes the steering wheel at first is not properly absorbed.
In this manner, the problem in that the initial shock is not properly absorbed resides in that the first step of giving the shock to the driver is performed in a very short time. To be more specific, the quantity of shock is determined by product of the magnitude of shock and the time of shock. Here, when the quantities of shocks are identical to each other, the longer the time of shock becomes, the smaller the magnitude of shock becomes in proportion to the lengthened time of shock.
Further, the conventional structure as above has another problem in that, when the partition member 4 formed at the slot A1 is not deformed, the shock is not absorbed at all. This phenomenon may occur when the driver strikes the steering wheel in a relatively weak manner, when the shock is released to a certain extent by an airbag, or so forth.